Because we live in an era of rapid technological change, we are used to (if not necessarily comfortable with) the idea of obsolescence. When I started my first job as an engineer, our office relied on a mini-computer for heavy-duty analysis, and on paper and calculators for everything else. We had one phone for every four designers, one fax machine for the office, and no micro-computers. Today, every engineer at Old Structures has a desktop computer more powerful than the room-filling mini of 26 years ago, we use cell-phones often and faxes almost never, and we go on site carrying hand-held computers.
Structural technology changes at a slower pace (note 1) than computers but it still changes. The steel we specify for common beams is significantly stronger than that of twenty years ago, we have new additives that greatly improve concrete quality, and we have more accurate models of loading. Every time a building code is changed (note 2) and every time a material code is updated (note 3), some pieces of the old code are made obsolete. The changes may be minor or may substantially change the way in which we perform some aspects of analysis and design. Examples are easy to find: egress requirements were made more stringent after the 1911 Triangle fire and the 1942 Cocoanut Grove fire. A structural example that is obscure to non-engineers but that plays an import role in our reanalysis of existing steel-frame buildings is that the “K” factor giving effective lengths for steel columns was not introduced not ordinary design until the sixth edition of the AISC manual in 1963.
In short, as our buildings age so does their technology. Each change to a statutory building code, each change to the materials that are manufactured, and each change to code-specific materials moves us further from what we previously designed and built. The aging of technology is inevitable, leaving only one question: does it matter?
Here is an 1893 picture (note 4) of high-tech construction as designed by some of the best engineers around. That high-tech is also obsolete and something that we would never use today. So does it matter? Good or bad? The building shown, the Manhattan Life Building at 66 Broadway in New York, was demolished in the 1960s, so we can discuss safety issues in a purely theoretical sense. The caisson foundations and riveted steel frame of Manhattan Life, if analyzed using current codes, are extremely conservative and would be considered safe for occupancy loads, wind loads, and even the seismic loading that no one at the time of its construction considered to be an issue in New York. The unreinforced-masonry facade is now known to provide inadequate protection to the steel against water infiltration and would likely lose chunks into the street during an earthquake because of the large amounts of projecting ornament supported only by masonry cantilevers. The terra-cotta tile arch floors can function as diaphragms but, being brittle, might suffer local failures during an earthquake.
In short, the building is a mixture of obsolete technology that we consider to be over-designed (and therefore safe) and obsolete technology that we consider to be under-designed (and therefore unsafe). Most building codes (and specifically the NYC code) typically allow existing buildings that are in good condition to remain in use regardless of the presence of obsolete structural technology. So if the Manhattan Life building still existed, it would almost certainly be packed with tenants who would be ignorant of their encouragement of obsolescence. And, barring an earthquake unprecedented in New York and outside of the design standards of the building code, their ignorance would be rewarded with a level of safety comparable to most modern buildings.
1 The slower pace is a sign of a mature technology. Between 1885 and 1925, structural technology changed at a pace similar to that of electronics today.
2 Such as the 2008 introduction of a new New York City Building Code based on the International Building Code.
3 The 14th edition of the Steel Construction Manual was published in 2011.
4 William Birkmire, The Planning and Construction of High Office Buildings, second edition (1900), figure 18, page 46.